Stromal vascular cells from epididymal fat pads of lean and obese mice were cultured in a medium (α‐MEM) containing fetal bovine serum (FBS) and cell replication followed for 11 days. In both types of cells, confluence occurred at 4–5 days, after which virtual growth arrest occurred in lean‐mouse cells while replication continued, albeit at a slower rate in obese‐mouse cells. Little or no lipid accumulation or glycerol‐3‐phosphate dehydrogenase (GPDH) activity was observed under these conditions. When a differentiation mixture consisting of insulin, corticosterone and isobutylmethylxanthine was added to the serum‐containing α‐MEM, a proportion of the lean‐mouse cells accumulated triglycerides and GPDH activity increased significantly, indicating differentiation. By contrast, little or no differentiation occurred in obese‐mouse cells. When cells grown in serum‐containing α‐MEM were transferred to a serum‐free defined medium at confluence, extensive differentiation and maturation occurred in lean‐mouse cells but not in obese‐mouse cells. Similar experiments were conducted in cells isolated from the retroperitoneal fat pad. Although the growth pattern was similar to that of epididymal preadipocytes, the retroperitoneal lean‐ and obese‐mouse cells differentiated more readily than epididymal cells, as shown by the GPDH specific activity. These data suggest that cells from obese mice are resistant to differentiation under conditions that support extensive differentiation in lean‐mouse cells.